Typically, vehicle steering racks are manufactured from round solid bar stock with the toothed region broached across the bar near one end. This results in the cross section of the toothed region having a ‘D’ shape and hence these racks are commonly referred to as “D-racks”.
An alternative method of manufacturing a steering rack from round solid bar stock is to forge the toothed region. An advantage of forging is that the teeth may be shaped to have a variable gear ratio. U.S. Pat. No. 4,571,982 (Bishop et al) and U.S. Pat. No. 5,862,701 (Bishop et al) disclose die apparatuses for flashless warm forging steering racks having a toothed region with a “Y” shaped cross section. These types of racks are known as “Y-racks”. A disadvantage of these die apparatuses is that they are only suited to forging Y-racks.
Warm forging of steel is well known. The actual temperature used for warm forging depends on the application, and can range from 600° C. to 1000° C. Temperatures in the range 650° C. to 800° C. are particularly well suited to forging precision net shape gear teeth that do not require finish machining.
WO 2005/053875 A1 (Bishop Innovation) discloses various die arrangements for flashless warm forging D-racks in particular. However, an improved die apparatus to implement some of the die arrangements disclosed in WO 2005/053875 A1 is desirable. In particular it is desirable to provide an improved die apparatus suited to forging “large offset” racks. Large offset racks have their teeth closer to the longitudinal centre line of the rack than typical D-racks. Large offset racks have wider teeth than typical D-racks, which makes them suited to column assist steering gears.
Another type of steering rack is the “V-rack”. These racks have a cross section having a ‘V’ shape. An improved die apparatus suited to forging both D-racks and V-racks is also desirable.
It is an object of the present invention to provide an improved die apparatus for forging steering racks, or at least a useful alternative.